1. Field of the Invention
The present invention relates to a velocity detecting system, a velocity detecting method, a velocity detecting program, a position detecting system, a position detecting method and a position detecting program, and a navigation system, and is applicable to a navigation system to be installed in a mobile body, for example.
2. Description of the Related Art
Heretofore, a navigation system to be installed in a moving mobile body or the like in that the present position is calculated based on a GPS signal transmitted from a Global Positioning System (GPS) satellite, and the position and the forward direction of the above mobile body are displayed on a map screen has been widely popularized.
In such navigation system, the velocity and the forward direction of the mobile body are calculated using an acceleration sensor for detecting the acceleration of the mobile body in the forward direction and a gyro sensor (yaw rate sensor) for detecting the rotary angular velocity of the above mobile body in a horizontal direction. Thereby, the present position of the mobile body can be estimated even in the case where a GPS signal cannot be received in the shade of a building and in a tunnel, for example.
However, this acceleration sensor had a problem that when the mobile body is on a slope, it detects the acceleration including a forward direction component of gravity acceleration operating on the mobile body (hereinafter, this is referred to as a gravity acceleration component).
Then, some navigation systems in which when a GPS signal can be received, a gravity acceleration component is previously calculated from the value of acceleration calculated using the position that was calculated based on the above GPS signal and a detected value by an acceleration sensor, and when a GPS signal cannot be received, the velocity of the mobile body is calculated after the detected value by the acceleration sensor was corrected, in consideration of the above gravity acceleration component have been proposed (see Japanese Patent Laid-Open No. 3516126, for example).